Add libc dependency for unix targets

This commit adds the `libc` dependency to the `Cargo.toml` file for
Unix-based targets. This dependency is required by the `ffmpeg` command
execution within the `recorder` module, specifically for handling
process management and signaling on Unix-like systems.

client-desktop/src/state.rs

@@ -0,0 +1,46 @@
+//! UI-visible application state. Transitions are driven by user actions
+//! (buttons) and async events from the recorder + uploader channels.
+
+use std::time::Instant;
+
+use uuid::Uuid;
+
+#[derive(Debug)]
+pub enum AppState {
+    /// No valid config on disk — show settings panel.
+    NotConfigured,
+    /// Ready for a new recording. No ephemeral context.
+    Idle,
+    /// ffmpeg is actively capturing audio.
+    Recording {
+        case_id: Uuid,
+        recorded_at: String,
+        started_at: Instant,
+    },
+    /// User pressed Stop; waiting for ffmpeg to finalize the MOOV atom.
+    FinalizingRecording {
+        case_id: Uuid,
+        recorded_at: String,
+    },
+    /// File handed to uploader; waiting for server ACK.
+    Uploading {
+        case_id: Uuid,
+    },
+    /// Terminal error; user must dismiss or fix config.
+    Error {
+        message: String,
+    },
+}
+
+impl AppState {
+    pub fn label(&self) -> &'static str {
+        match self {
+            Self::NotConfigured => "Konfiguration fehlt",
+            Self::Idle => "Bereit",
+            Self::Recording { .. } => "Aufnahme läuft",
+            Self::FinalizingRecording { .. } => "Speichere…",
+            Self::Uploading { .. } => "Upload läuft",
+            Self::Error { .. } => "Fehler",
+        }
+    }
+}